Off-center deposition of organic semiconductor in an organic semiconductor device

ABSTRACT

The present disclosure provides a method of making a thin film semiconductor device such as a transistor comprising the steps of: a) providing a substrate bearing first and second conductive zones which define a channel therebetween, where the channel does not border more than 75% of the perimeter of either conductive zone; and b) depositing a discrete aliquot of a solution comprising an organic semiconductor adjacent to or on the channel, where a majority of the solution is deposited to one side of the channel and not on the channel. In some embodiments of the present disclosure, the solution is deposited entirely to one side of the channel, not on the channel, and furthermore the solution is deposited in a band having a length that is less than the channel length. The present disclosure additionally provides thin film semiconductor devices such as a transistors.

FIELD OF THE DISCLOSURE

This invention relates to the manufacture of organic semiconductordevices by inkjet printing or similar fluid deposition processes and thedevices so made.

BACKGROUND OF THE DISCLOSURE

In recent years there has been an increasing research effort aimed atusing organic materials as semiconductors rather than the traditionalinorganic materials such as silicon and gallium arsenide. Among otherbenefits, the use of organic materials may enable lower costmanufacturing of electronic devices, may enable large area applications,and may enable the use of flexible substrates as supports for electroniccircuitry in display backplanes, integrated circuits RFID tags, andsensors.

A variety of organic semiconductor materials have been considered, themost common being fused aromatic ring compounds as exemplified byacenes. At least some of these organic semiconductor materials haveperformance characteristics such as charge-carrier mobility, on/offcurrent ratios, and sub-threshold voltages that are comparable orsuperior to those of amorphous silicon-based devices. These materialshave often been vapor deposited since they are not very soluble in mostsolvents. When organic semiconductors have been deposited from solution(such as in a solution with an organic solvent), good or optimumperformance characteristics have been difficult to achieve.

U.S. Pat. No. 6,690,029 B1 purportedly discloses certain substitutedpentacenes and electronic devices made therewith.

WO 2005/055248 A2 purportedly discloses certain substituted pentacenesand polymers in top gate thin film transistors.

U.S. patent application Ser. No. 11/275,366 filed Dec. 28, 2005, thedisclosure of which is incorporated herein by reference, generallydiscloses an all-inkjet printed thin film transistor and methods ofmaking and using same. The following references may be relevant toinkjet printing of organic semiconductors: Lim et al, “Self-Organizationof Ink-jet-Printed Triisopropylsilylethynyl Pentacene viaEvaporation-Induced Flows in a Drying Droplet,” Adv. Funct. Mater.,2008, 18, pp. 229-234.

Some report using unusual device geometries with organic semiconductormaterials, e.g. concentric ring or Corbino geometries. The followingreferences may be relevant to such a technology: Klauk et al.,“Pentacene Organic Thin-Film Transistors for Circuit and DisplayApplications,” IEEE Transactions on Electron Devices, Vol. 46, No. 6,June 1999, pp. 1258-1263; Meijer et al., “Dopant density determinationin disordered organic field-effect transistors,” J. App. Physics, Vol.93, No. 8, 15 Apr. 2003, pp. 4831-4835.

U.S. patent application Ser. No. 11/275,367, filed Dec. 28, 2005, thedisclosure of which is incorporated herein by reference, generallydiscloses thin film transistor with bottom-gate geometry and methods ofmaking and using same.

U.S. Provisional Pat. App. No. 61/057,715, filed May 30, 2008, thedisclosure of which is incorporated herein by reference, generallydiscloses silylethynyl pentacenes, compositions containing silylethynylpentacenes, and methods of making and using silylethynyl pentacenes,e.g. as organic semiconductors.

U.S. Provisional Pat. App. No. 61/060,595, filed Jun. 11, 2008, thedisclosure of which is incorporated herein by reference, generallydiscloses the use of mixed solvent systems for deposition of organicsemiconductors.

U.S. Provisional Pat. App. No. 61/076,186, filed Jun. 27, 2008, thedisclosure of which is incorporated herein by reference, generallydiscloses methods of growing organic semiconductive layers; methods offabricating organic semiconductor devices; and layers and devices formedthereby.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a method of making a thin filmsemiconductor device comprising the steps of: a) providing a substratebearing first and second conductive zones, wherein the first and secondconductive zones define a channel therebetween, and wherein the channeldoes not border more than 75% or in some embodiments 50% of theperimeter of either conductive zone; and b) depositing a discretealiquot of a solution comprising an organic semiconductor adjacent to oron the channel, where the aliquot provides organic semiconductor to asingle thin film semiconductor device, where a majority of the solutionis deposited to one side of the channel and not on the channel. In someembodiments the boundaries between the channel and each of theconductive zones are substantially linear and substantially parallel. Insome embodiments the thin film semiconductor device is a transistor, thefirst conductive zone is a source and the second conductive zone is adrain. In some embodiments more than 60% of the solution is deposited toone side of the channel and not on the channel, in some more than 70%,in some more than 80%, in some more than 90%, in some 100%. In someembodiments the discrete aliquot is deposited in the form of a pluralityof droplets, typically by inkjet printing. In some such embodiments, atleast 60% of the droplets are deposited to one side of and not on thechannel, in others at least 70%, in others at least 80%, in others atleast 90%, in others 100% In some embodiments, the discrete aliquot of asolution comprising an organic semiconductor is allowed to wet out afterdeposition and thereupon has a length that is not more than 10 times thechannel length. In some embodiments, the discrete aliquot of a solutioncomprising an organic semiconductor is deposited in a band having alength that is less than the channel length.

In some embodiments of the present disclosure, the discrete aliquot of asolution comprising an organic semiconductor is deposited entirely toone side of the channel, not on the channel, and furthermore thesolution is deposited in a band having a length that is less than thechannel length. Such a method not only functions but provides improvedresults.

The present disclosure additionally provides a thin film semiconductordevice, which comprises: a) a substrate bearing first and secondconductive zones, wherein the first and second conductive zones define achannel therebetween, and wherein the channel does not border more than75% or in some embodiments 50% of the perimeter of either conductivezone; and b) a discrete semiconductor layer comprising an organicsemiconductor on and adjacent to the channel, where the discretesemiconductor layer serves a single thin film semiconductor device,where a majority of the discrete semiconductor layer lies to one side ofand not on the channel. In some embodiments the boundaries between thechannel and each of the conductive zones are substantially linear andsubstantially parallel. In some embodiments the thin film semiconductordevice is a transistor, the first conductive zone is a source and thesecond conductive zone is a drain. In some embodiments, the deviceadditionally comprises a gate and a dielectric layer. In someembodiments, more than 55% of the discrete semiconductor layer lies toone side of and not on the channel, in others more than 60%, in othersmore than 65%, in others more than 70%, in others more than 75%, inothers more than 80%. In some embodiments the discrete semiconductorlayer has a length that is not more than 10 times the channel length.

The present disclosure additionally provides a method of making a thinfilm semiconductor device pair comprising the steps of: a) providing asubstrate bearing i) first and second conductive zones, wherein thefirst and second conductive zones define a first channel therebetween;and ii) third and fourth conductive zones, wherein the third and fourthconductive zones define a second channel therebetween; and b) depositinga discrete aliquot of a solution comprising an organic semiconductoradjacent to or on the first and second channels, where the aliquotprovides organic semiconductor to exactly two single thin filmsemiconductor devices, where a majority of the solution is deposited toone side of the first channel and not on the first channel, and where amajority of the solution is deposited to one side of the second channeland not on the second channel.

The present disclosure additionally provides a thin film semiconductordevice pair comprising: a) a substrate bearing i) first and secondconductive zones, wherein the first and second conductive zones define afirst channel therebetween; and ii) third and fourth conductive zones,wherein the third and fourth conductive zones define a second channeltherebetween; and b) a discrete semiconductor layer comprising anorganic semiconductor on and adjacent to the first and second channels,where the discrete semiconductor layer serves exactly two single thinfilm semiconductor devices, where a majority of the discretesemiconductor layer lies to one side of and not on the first channel,and where a majority of the discrete semiconductor layer lies to oneside of and not on the second channel.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a photomicrograph of an inkjet-printed thin film transistoraccording to the present disclosure, further described in Example 1.

FIG. 2 is a schematic drawing of an inkjet-printed thin film transistoraccording to the present disclosure based on the photomicrograph of FIG.1.

FIG. 3 is a photomicrograph of a comparative inkjet-printed thin filmtransistor, further described in Comparative Example 2C.

FIG. 4 is a photomicrograph of an all inkjet-printed backplane, furtherdescribed in Example 1.

FIG. 5 is a schematic representation of a matrix of pixels designed toinkjet-print a discrete aliquot of organic semiconductor solution,further described in Example 1 and Comparative Example 2C.

FIG. 6 is a graph presenting mobility values for transistors of Example1 and Comparative Example 2C.

FIG. 7 is a graph presenting sub-threshold voltage values fortransistors of Example 1 and Comparative Example 2C.

FIG. 8 is a graph presenting on/off current values for transistors ofExample 1 and Comparative Example 2C.

DETAILED DESCRIPTION

The present disclosure provides a method of making a thin filmsemiconductor device comprising the steps of: a) providing a substratebearing first and second conductive zones, wherein the first and secondconductive zones define a channel therebetween and wherein the channeldoes not border more than 75% of the perimeter of either conductivezone; and b) depositing a discrete aliquot of a solution comprising anorganic semiconductor adjacent to or on the channel, where the aliquotprovides organic semiconductor to a single thin film semiconductordevice, where a majority of the solution is deposited to one side of thechannel and not on the channel. The present disclosure additionallyprovides a thin film semiconductor device, which comprises: a) asubstrate bearing first and second conductive zones, wherein the firstand second conductive zones define a channel therebetween, and whereinthe channel does not border more than 75% of the perimeter of eitherconductive zone; and b) a discrete semiconductor layer comprising anorganic semiconductor on and adjacent to the channel, where the discretesemiconductor layer serves a single thin film semiconductor device,where a majority of the discrete semiconductor layer lies to one side ofand not on the channel.

The thin film device may be any suitable semiconductor device, includingdiodes, triodes such as transistors, or other multi-terminal devices.Most typically the device is a transistor. Where the device is atransistor, the first conductive zone is typically a source electrodeand the second conductive zone is typically a drain electrode. Thetransistor typically includes a gate electrode. The transistor typicallyincludes a dielectric layer interposed between the gate and thesemiconductor layer.

The thin film device may have any suitable geometry, including topcontact/bottom gate, bottom contact/bottom gate, top contact/top gate orbottom contact/top gate geometries disclosed in U.S. patent applicationSer. No. 11/275,367, filed Dec. 28, 2005, the disclosure of which isincorporated herein by reference. In some embodiments, the thin filmdevice has top contact/bottom gate geometry. In some embodiments, thethin film device has bottom contact/bottom gate geometry. In someembodiments, the thin film device has top contact/top gate geometry. Insome embodiments, the thin film device has bottom contact/top gategeometry.

With reference to FIG. 2, in some embodiments the device according tothe present disclosure comprises a channel 50 having length A and widthB bordered by two conductive zones 10 and 20. Please note that,following standard terminology in the art, the word “length” designatesthe distance between the conductive zones even when it is the smallerdimension of the channel, i.e., smaller than the “width.” Where thedevice is a transistor, these conductive zones 10 and 20 are typicallythe source and drain electrodes. In the embodiment depicted in FIG. 2,the device is built on a substrate 60 with bottom contact/bottom gategeometry. In this geometry, a conductive layer patterned to form gate 30is applied to substrate 60 followed by a dielectric layer (which istransparent in FIG. 1 and therefore not visible in FIG. 2), a secondconductive layer patterned to form source and drain 10 and 20, andfinally discrete semiconductor layer 40.

With reference to FIG. 2, the channel length A is the distance acrossthe channel 50 from one conductive zone 10 to the other conductive zone20. Typically, the channel length is substantially constant. In someembodiments, a substantially constant channel length is constant bydesign and varies only by reason of material variation and externalconditions. In some embodiments, a substantially constant channel lengthis constant +/−25%, in other embodiments +/−20%, in other embodiments+/−15%, in other embodiments +/−10%, in other embodiments +/−5%, inother embodiments +/−2.5%, in other embodiments +/−1%.

With reference to FIG. 2, the discrete semiconductor layer 40 has alength C which is about 5 times channel length A. Please note that, theword “length” designates the dimension of the discrete semiconductorlayer 40 that is the parallel to the length of the channel, even when itis the smaller dimension of discrete semiconductor layer 40, i.e.,smaller than the “width.” In some embodiments, length C of the discretesemiconductor layer 40 is between 2 and 50 times channel length A. Insome embodiments, length C of the discrete semiconductor layer 40 isbetween 3 and 20 times channel length A. In some embodiments, length Cof the discrete semiconductor layer 40 is between 4 and 10 times channellength A.

In some embodiments, the channel width is taken to be that width overwhich the channel has a substantially constant channel length. In someembodiments, the channel width is taken to be that width over which thechannel overlays a gate electrode. In some embodiments, the channelwidth is taken to be that width over which the channel is spanned bysemiconductor material. In some embodiments, the channel width is takento be that width over which the channel meets some combination of thepreceding conditions. In some embodiments, including that depicted inFIG. 2, channel width B is taken to be that width over which the channel50 meets all three conditions: overlaying gate electrode 30, having asubstantially constant channel length A and being spanned bysemiconductor material. In the embodiments depicted in FIG. 2, channelwidth B terminates at its upper end where channel 50 is not spanned bysemiconductor material and channel width B terminates at its lower endwhere channel 50 does not have substantially constant channel length A.

In some embodiments, the boundaries between the channel 50 and each ofthe conductive zones 10 and 20 are substantially linear, substantiallyparallel, or both.

For the purpose of this disclosure, conductive zones are distinguishedfrom vias or conductive traces which may be electrically connected tothe conductive zones. In some embodiments, the conductive zones may bedefined to be only such parts of source or drain electrodes that overlaya gate electrode. The channel does not border more than 75% of theperimeter of either conductive zone. The channel of the device accordingto the present disclosure does not form a concentric ring geometry orCorbino geometry. In some embodiments, the channel does not border 60%or more of the perimeter of either conductive zone. In some embodiments,the channel does not border 50% or more of the perimeter of eitherconductive zone. In some embodiments, the channel does not border 40% ormore of the perimeter of either conductive zone.

With reference to FIG. 2, in some embodiments the device according tothe present disclosure comprises a discrete semiconductor layer 40comprising an organic semiconductor. The discrete semiconductor layer 40is located adjacent to or on the channel 50, where a majority of thediscrete semiconductor layer 40 lies to one side of and not on thechannel 50. As used herein, “to one side” means to a single side of thechannel and not directly over the channel. In the embodiment depicted inFIG. 2, it can be seen that a major axis midline of the oval shape ofthe discrete semiconductor layer 40 lies over conductive zone 10 and notover channel 50, and therefore it may be concluded that a majority ofthe discrete semiconductor layer 40 lies to one side of and not on thechannel 50; that is, a majority of the lateral area of the discretesemiconductor layer 40 lies to one side, where the lateral area is thearea projected to a plane parallel to the substrate. In some embodimentsmore than 55% of the discrete semiconductor layer lies to one side ofand not on the channel, in other embodiments more than 60%, in otherembodiments more than 65%, in other embodiments more than 70%, in otherembodiments more than 75%, in other embodiments more than 80%, in otherembodiments more than 85%, in other embodiments more than 90%. Notethat, for the purpose of this determination, the channel is consideredto be unbounded in width.

In an alternate embodiment, a discrete semiconductor layer serves eachof two back-to-back thin film semiconductor devices. In suchembodiments, the discrete semiconductor layer is located between thechannels of the two back-to-back thin film semiconductor devices. Withregard to each of the two channels, a majority of the discretesemiconductor layer lies to one side of and not on the channel. In someembodiments more than 55% of the discrete semiconductor layer lies toone side of and not on each channel, in other embodiments more than 60%,in other embodiments more than 65%, in other embodiments more than 70%,in other embodiments more than 75%, in other embodiments more than 80%,in other embodiments more than 85%, in other embodiments more than 90%.In such an embodiment, the discrete semiconductor layer may later beseparated into two portions, each serving one device. The separation maybe by any suitable means, including cutting or scoring by knife, laser,or the like, or chemical means to remove or render non-conductive acenter portion of the discrete semiconductor layer.

The discrete semiconductor layer includes an organic semiconductormaterial. Any suitable organic semiconductor material may be used,including those described in U.S. Pat. No. 6,690,029, U.S. patentapplication Ser. No. 11/275,366, filed Dec. 28, 2005, U.S. patentapplication Ser. No. 11/275,367, filed Dec. 28, 2005, U.S. ProvisionalPat. App. No. 61/057,715, filed May 30, 2008, U.S. Provisional Pat. App.No. 61/060,595, filed Jun. 11, 2008, the disclosures of which areincorporated herein by reference. The semiconducting material may be afunctionalized pentacene compound according to Formula I:

where each R¹ is independently selected from H and CH₃ and each R² isindependently selected from branched or unbranched, linear or cyclicC2-C18 alkanes, branched or unbranched C1-C18 alkyl alcohols, branchedor unbranched, linear or cyclic C2-C18 alkenes, C4-C8 aryls orheteroaryls, C5-C32 alkylaryl or alkyl-heteroaryl, a ferrocenyl, or SiR³₃ where each R³ is independently selected from hydrogen, branched orunbranched C1-C10 alkanes, branched or unbranched, linear or cyclicC1-C10 alkyl alcohols or branched or unbranched C2-C10 alkenes.Typically each R¹ is H. Typically, each R² is SiR³ ₃. More typicallyeach R² is SiR³ ₃ and each R³ is independently selected from branched orunbranched, linear or cyclic C1-C10 alkanes or alkenes. Most typically,the compound is 6,13-bis(triisopropylsilylethynyl)pentacene(TIPS-pentacene), shown in formula II:

In some embodiments, each R² is independently selected from —SiR⁴ _(x)R⁵_(y)R⁶ _(z), wherein:

each R⁴ independently comprises (i) a branched or unbranched,substituted or unsubstituted C1-C8 alkyl group, (ii) a substituted orunsubstituted cycloalkyl group, or (iii) a substituted or unsubstitutedcycloalkylalkylene 5 group; each R⁵ independently comprises (i) abranched or unbranched, substituted or unsubstituted C2-C8 alkenylgroup, (ii) a substituted or unsubstituted cycloalkyl group, or (iii) asubstituted or unsubstituted cycloalkylalkylene group; each R⁶ comprises(i) hydrogen, (ii) a branched or unbranched, substituted orunsubstituted C2-C8 alkynyl group, (iii) a substituted or unsubstitutedcycloalkyl group, (iv) a substituted or unsubstituted cycloalkylalkylenegroup, (v) a substituted aryl group, (vi) a substituted or unsubstitutedarylalkylene group, (vii) an acetyl group, or (viii) a substituted orunsubstituted heterocyclic ring comprising at least one of O, N, S andSe in the ring; x=1 or 2; y=1 or 2; z=0 or 1; and (x+y+z)=3.

The discrete semiconductor layer typically contains the compound ofFormula I or of Formula II in an amount of 0.1-99% by weight.

In some embodiments, the discrete semiconductor layer may includeadditional materials such as suitable polymers. In some embodiments, apolymer additive has a dielectric constant at 1 kHz of greater than 1.0,more typically greater than 3.3, more typically greater than 3.5, andmore typically greater than 4.0. The polymer typically has a M.W. of atleast 1,000 and more typically at least 5,000. Typical polymers includepoly(4-cyanomethyl styrene) and poly(4-vinylphenol). In someembodiments, cyanopullulans may also be used.

Typical polymers also include those described in U.S. Patent PublicationNo. 2004/0222412 A1, incorporated herein by reference. Polymersdescribed therein include substantially nonfluorinated organic polymershaving repeat units of the formulas:

wherein:

each R¹ is independently H, Cl, Br, I, an aryl group, or an organicgroup that includes a crosslinkable group;

each R² is independently H, an aryl group, or R⁴;

each R³ is independently H or methyl;

each R⁵ is independently an alkyl group, a halogen, or R⁴;

each R⁴ is independently an organic group comprising at least one CNgroup and having a molecular weight of about 30 to about 200 per CNgroup; and

n=0-3;

with the proviso that at least one repeat unit in the polymer includesan R⁴.

Other polymers which may be used may also include polystyrene, polyα-methylstyrene), poly(α-vinylnaphthalene), poly(vinyltoluene),polyethylene, cis-polybutadiene, polypropylene, polyisoprene,poly(4-methyl-1-pentene), poly(4-methylstyrene),poly(chorotrifluoroethylene), poly(2-methyl-1,3-butadiene),poly(p-xylylene), poly(α-α-α′-α′ tetrafluoro-p-xylylene),poly[1,1-(2-methyl propane) bis(4-phenyl)carbonate], poly(cyclohexylmethacrylate), poly(chlorostyrene), poly(2,6-dimethyl-1,4-phenyleneether), polyisobutylene, poly(vinyl cyclohexane), poly(vinylcinnamate),poly(4-vinylbiphenyl), poly(1,2-butadiene), polyphenylene, poly(methylmethacrylate), and polyvinyl phenol.

Copolymers of the above materials may also be useful. For example,polymers of styrene and α-methyl styrene; copolymers including styrene,α-methylstyrene and butadiene, for example. Both random or blockcopolymers can be used. Exemplary copolymers include, but are notlimited to, poly(ethylene/tetrafluoroethylene);poly(ethylene/chlorotrifluoro-ethylene); fluorinated ethylene/propylenecopolymer; polystyrene-co-α-methylstyrene; ethylene/ethyl acrylatecopolymer; poly(styrene/10% butadiene); poly(styrene/15% butadiene);poly(styrene/2,4 dimethylstyrene); cyclic olefin copolymers such asthose commercially available from Dow Chemical under the tradedesignation TOPAS (all grades); branched or non-branchedpolystyrene-block-polybutadiene; polystyrene-block(polyethylene-ran-butylene)-block-polystyrene;polystyrene-block-polybutadiene-block-polystyrene;polystyrene-(ethylene-propylene)-diblock-copolymers (e.g. KRATON-G1701E,Kraton Polymers U.S. LLC, Houston, Tex.); poly(propylene-co-ethylene);and poly(styrene-co-methylmethacrylate).

The discrete semiconductor layer may contain the polymer in an amount of0-99.9% by weight, more typically 10-90% by weight, more typically20-50% by weight.

In the method of the present disclosure, a discrete aliquot of asolution comprising an organic semiconductor is deposited adjacent to oron the channel. In a typical embodiment, each such aliquot providesorganic semiconductor to a single thin film semiconductor device.

Any suitable organic semiconductor may be used, as discussed above.

In some embodiments, the solution may additionally include a polymersuch as discussed above. In some embodiments, a semiconductor crystalgrowth solution may be used, as disclosed in U.S. Provisional Pat. App.No. 61/076,186, filed Jun. 27, 2008, the disclosure of which isincorporated herein by reference.

Any suitable solvent may be used, which may include ketones, aromatichydrocarbons, and the like, and may include mixtures thereof. Typicallythe solvent is organic. Typically the solvent is aprotic. Suitablesolvents may include, but are not limited to, toluene, ethylbenzene,butylbenzene, chlorobenzene, dichlorobenzene, anisole,tetrahydronaphthalene, cyclohexanone and mixtures thereof. In somesingle solvent embodiments, the solution comprises at least 95% byweight of a single solvent.

Mixed solvent systems may be used, as disclosed in U.S. Provisional Pat.App. No. 61/060,595, filed Jun. 11, 2008, the disclosure of which isincorporated herein by reference.

Any suitable amount of organic semiconductor may be deposited in themethod of the present disclosure or present in the device of the presentdisclosure. Greater amounts may generate thicker and/or more crystallinesemiconductor layers in the final device. In some embodiments, thevolume of the discrete aliquot of solution comprising an organicsemiconductor is between 15 pL and 40 nL. In some embodiments, thevolume of the discrete aliquot of solution comprising an organicsemiconductor is at least 15 pL, more typically at least 25 pL, moretypically at least 50 pL, more typically at least 250 pL, and in someembodiments 500 pL or more. In some embodiments, the volume of thediscrete aliquot of solution comprising an organic semiconductor is notmore than 40 nL, more typically not more than 10 nL, more typically notmore than 4 nL, more typically not more than 1 nL.

In the method of the present disclosure, the discrete aliquot of asolution comprising an organic semiconductor may be deposited by anysuitable method. In some embodiments, the discrete aliquot is depositedas a single drop or droplet. Such embodiments may include inkjetprinting, micropipetting, flexographic printing, and the like. In someembodiments, the discrete aliquot is deposited in the form of aplurality of droplets. Such embodiments also may include inkjetprinting, micropipetting, flexographic printing, and the like.

Inkjet printing is well known, e.g., for printing graphics, includingmulti-color graphics. Inkjet printing enables precise positioning ofvery small drops of ink. Any suitable inkjet printing system may be usedin the practice of the present invention, including thermal,piezoelectric, and continuous inkjet systems. Most typically apiezoelectric inkjet system is used Inks useful in inkjet printing aretypically free of particulates greater than 500 nm in size and moretypically free of particulates greater than 200 nm in size.

In the method of the present disclosure, the discrete aliquot of asolution comprising an organic semiconductor is deposited adjacent to oron the channel, with a majority of the solution deposited to one side ofthe channel and not on the channel. As used herein, “to one side” meansto a single side, outside the channel. As used herein, the location ofdeposition is the initial location of deposition notwithstandingsubsequent flow or wetting out. In some embodiments of the methodaccording to the present disclosure, more than 55% of the solution isdeposited to one side of the channel and not on the channel, in otherembodiments more than 60%, in other embodiments more than 65%, in otherembodiments more than 70%, in other embodiments more than 75%, in otherembodiments more than 80%, in other embodiments more than 85%, in otherembodiments more than 90%, in other embodiments more than 95%. In someembodiments all of the solution is deposited to one side of the channeland not on the channel. In embodiments where the discrete aliquot isdeposited in the form of a plurality of droplets, which may includeinkjet printing, more than 50% of the droplets are deposited to one sideof the channel and not on the channel, in other embodiments more than55%, in other embodiments more than 60%, in other embodiments more than65%, in other embodiments more than 70%, in other embodiments more than75%, in other embodiments more than 80%, in other embodiments more than85%, in other embodiments more than 90%, in other embodiments more than95%. In some embodiments all of the droplets are deposited to one sideof the channel and not on the channel.

In some embodiments of the method according to the present disclosure,the discrete aliquot of a solution comprising an organic semiconductorhas a length, after deposition and wetting out on the surface, which isabout 5 times the channel length. In some embodiments, the length isbetween 2 and 50 times the channel length. In some embodiments, thelength is between 3 and 20 times the channel length. In someembodiments, the length is between 4 and 10 times the channel length.

In some embodiments of the method according to the present disclosure,inkjet printed layers such as the gate, dielectric, source/drain andsemiconductor layers are printed from images, typically comprised ofrectilinear matrices of pixels, which determine the deposit locationsfor the inkjet deposited solutions. In some embodiments of the methodaccording to the present disclosure, the image of the deposit locationfor the solution comprising the organic semiconductor has a lengthbetween 0.05 and 5 times the channel length. Please note again that theword “length” designates the dimension that is the parallel to thelength of the channel, even when the length of the image of the depositlocation is the smaller dimension, i.e., smaller than the “width.” Insome embodiments of the method according to the present disclosure, theimage of the deposit location for the solution comprising the organicsemiconductor has a length that is less than the channel length. In someembodiments of the method according to the present disclosure, the imageof the deposit location for the solution comprising the organicsemiconductor has a length that is less than one half the channellength. In some embodiments of the method according to the presentdisclosure, the image of the deposit location for the solutioncomprising the organic semiconductor has a length between 0.1 and 0.9times the channel length. In some embodiments of the method according tothe present disclosure, the deposit location for the solution comprisingthe organic semiconductor has a length between 0.05 and 5 times thechannel length. In some embodiments of the method according to thepresent disclosure, the deposit location for the solution comprising theorganic semiconductor has a length that is less than the channel length.In some embodiments of the method according to the present disclosure,the deposit location for the solution comprising the organicsemiconductor has a length that is less than one half the channellength. In some embodiments of the method according to the presentdisclosure, the deposit location for the solution comprising the organicsemiconductor has a length between 0.1 and 0.9 times the channel length.

It follows from the preceding that, in some embodiments of the methodaccording to the present disclosure, the solution comprising the organicsemiconductor is deposited entirely outside of the channel and depositedin a band having a length that is less than the channel length.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

EXAMPLES

Unless otherwise noted, all reagents were obtained or are available fromAldrich Chemical Co., Milwaukee, Wis., or may be synthesized by knownmethods.

Examples 1 and 2C

A sheet containing two backplanes was fabricated by inkjet printingevery layer—gate, dielectric, source/drain and semiconductor—onto aflexible polymeric substrate by the process described below. Eachbackplane contained 8 rows and 15 columns of transistors (120 transistortotal) at a pitch of 3.0 mm. FIG. 4 is a digital photograph of one ofthe inkjet-printed backplanes.

The first of the two backplanes, Example 1, represented the presentdisclosure and the second, Comparative Example 2C, was comparative.

Each inkjet printed layer—gate, dielectric, source/drain andsemiconductor—was printed from an image created in Adobe® Photoshop®(Adobe Systems, San Jose, Calif.). Each image was created as arectilinear matrix of pixels for use with a 702 dpi (276 pixels per cm)print system. Thus, each pixel had an initial width of 36.2 microns.

The source/drain layer image included transistor channels having achannel length of 6 pixels, or 217 microns. As printed, the source/drainlayer material wetted out laterally, reducing the channel length toapproximately 128 microns in the printed backplane. Average measuredchannel length for Examples 1 and 2C were 120 microns and 136 microns,respectively. Average measured channel width for Examples 1 and 2C were780 microns and 910 microns, respectively.

The semiconductor layer image was designed to deposit discrete aliquotsof organic semiconductor solution, each providing organic semiconductorto a single transistor. FIG. 5 schematically represents thesemiconductor image used for each aliquot, which was 25 pixels in widthand 2 pixels in length and included 18 printed pixels representing 18drops of organic semiconductor solution deposited on the backplane. Eachdrop had a volume of 30 pL, for a total volume of 540 pL. As printed,this matrix of drops wetted out laterally to form a single continuousdeposit, roughly oval in shape, having a width of approximately 1200microns and a length of approximately 650 microns. These deposits arevisible as translucent ovals in both of FIGS. 1 and 3 and represented byindex number 40 in FIG. 2, which is based on FIG. 1.

In the backplane of Comparative Example 2C, the width of thesemiconductor image was centered over the width of the channel. FIG. 3is a photomicrograph of one transistor in the backplane of ComparativeExample 2C.

In the backplane of Example 1, the width of the semiconductor image wasoffset from the center of the channel by five pixels, or about 180microns. The offset was made in the design of the semiconductor imageitself and not in the printing process. It follows that none of thesemiconductor solution was deposited directly in the channel by inkjetprinting. Instead, the printed matrix of drops wetted out laterally toform a single continuous deposit which extended across the channel. FIG.1 is a photomicrograph of one transistor in the backplane of Example 1.

Inspection of FIGS. 1 and 3 suggests that the edge of each depositexhibited a strong crystalline morphology while the center wasamorphous. Thus, the offset semiconductor deposit in Example 1 appearsto position a substantial amount of crystalline material over thechannel. Inspection of FIGS. 1 and 3 suggests that a rectangularsemiconductor layer image, resulting in an oval deposit of semiconductormaterial, exhibits more parallelism of crystalline structure down itslong side than its short side. Thus, generating a long side andpositioning the long side over the channel as in Example 1 appears toposition more parallel crystalline material over the channel in achannel-crossing direction. Transistors of Example 1 demonstrateddramatically improved mobility over transistors of Comparative Example2C, as described in the quantitative test results which follow theprocess description below.

Process

An 8″×8″ piece of DuPont Teonex® Q65 4 mil thick PEN film was fastenedbetween two pieces of stainless steel. The two pieces of stainless steelclamp around the perimeter of the PEN film. These clamps help minimizethe shrinkage in the PEN film throughout the process. Both sides of theclamped PEN film were cleaned numerous times with absolute ethanol inorder to reduce particle contamination and to provide a clean surfacewith a constant surface energy. After cleaning, the clamped film wasthen fastened with four screws into the XY deposition system on analuminum vacuum table. After the clamped film was placed in the systemit is cleaned one more time with ethanol.

A Spectra-Dimatix SX3-128 printhead was then inserted into the system.The SX3-128 printhead has 128 jets with a 10 pL drop volume. Theprinthead was filled with approximately 20.0 mL of Cabot Ag-IJ-G-100-S1inkjetable silver conductor ink. This material served as the gate layerof the backplane. Once the printhead was in the system the height andsabre angle were adjusted. The printhead height was adjusted toapproximately 1.0 mm above the surface of the PEN film. The sabre anglewas adjusted to give a desired resolution of 702 dpi. Upon completion ofthe aforementioned, the substrate was registered. The corner of thestainless steel clamp was used as the starting point or origin. From theorigin a 1.0 inch offset was set in the negative x and y direction. Thiswas the location where the printhead started printing the conductive inkor patterned gate layer.

Before the application of the conductive ink, the substrate waspre-shrunk. The purpose of pre-shrinking the substrate was for improvedregistration. Shrinking of the film between the thermal curing of eachlayer affects registration of subsequent layers. The pre-shrinkingprocess included thermally heating the film from the bottom and the topof the substrate. Heating from below was done with an online hot plateset to 125° C. Heating from above the substrate was done with a 500Watt/inch infrared lamp. Once the hot plate reached 125° C., the IR lampscanned over the substrate 5 times with a velocity of 2.0 in./sec and ata 100% power level. This process took 25 seconds and the maximumtemperature of the substrate reached 140° C., which was recorded by aninfrared pyrometer.

Upon completion of the pre-shrinking process, the substrate/aluminumplaten was cooled to a temperature of 45° C. in preparation fordeposition of the silver gate layer. Printing the silver ink while theplaten is at an elevated temperature prevents the silver ink fromwetting out excessively on the PEN film substrate. Once the patternedgate layer is deposited onto the substrate it sat at 45° C. for 5.0minutes. This allowed the material to settle, thus producing a moreuniform layer for subsequent deposition processes.

After the silver sat for 5.0 minutes, it was sintered with the onlinehot plate and infrared lamp. The hot plate was set to 125° C. and thenthe IR lamp scanned over the patterned image 5 times at a velocity of2.0 in/sec. and at 100% power. The purpose of heating the substrate to125° C. before sintering the silver with the IR lamp was to decrease thesintering time. It took approximately 25 seconds to sinter the silverwith the IR lamp.

After the silver was sintered, the temperature of the hot plate was setto 150° C. The substrate remained at this temperature for 10 minutes.The purpose of this step was to verify all of the solvent is out of thesilver nanoparticle ink, which is 20% Ag, 40% ethanol and 40% ethlyeneglycol.

The next layer in the fabrication of the all-inkjet printed backplanewas the dielectric layer. After thermally curing the gate layer, theSX3-128 printhead was removed and replaced with a Spectra-Dimatix SE-128printhead. This printhead was used for printing the dielectric material,which was a zirconia acrylate in isophorone. The SE-128 has 128 jets anda 30 pL drop volume. The height was set to approximately 1.0 mm abovethe substrate and the sabre angle was set to produce a resolution of 702dpi. The platen temperature was reduced to 26° C. Printing thedielectric layer at too high of a temperature reduces wetting.Insufficient wetting produces holes in the dielectric layer, which canlead to undesired shorts in the thin-film transistors.

Before printing the dielectric layer, a test print was printed forregistering the dielectric layer relative to the patterned gate layer.The test print was compared to another test print that was printed withthe gate layer. The measured difference between the two test printsdetermined where printing of the dielectric layer began.

Once registration is completed a blanket coat of dielectric material wasprinted onto the gate layer. Upon completion of printing, the materialwas immediately dried, cured and dried again. The first drying processor pre-bake was done with the online hot plate and IR lamp. Once the hotplate reached a temperature of 75° C. the IR lamp scanned over theprinted image two times at a velocity of 2.0 in/sec and at 40% power.The IR step in this process was low temperature because increasing theintensity of this step could cause the dielectric layer to ‘skin over’and trap the solvent. Therefore, most of the drying was done thermallyfrom below the substrate. After the infrared lamp scanned over thesample, the platen temperature remained at 75° C. for an additional 10minutes. This step in the process was utilized for removing anyremaining solvent. After the solvent was removed from the dielectricmaterial it was cured or cross-linked at a platen temperature of 45° C.This was accomplished with a 250 nm wavelength UV germicidal lamp with anitrogen purge for 401 seconds. The final drying step or post-bake usedthe same process steps as the previously mentioned pre-bake except theIR lamp scanned over the image 5 times at 2.0 in./sec and at 100% power.

Upon completion of the dielectric layer, the SE-128 printhead wasremoved from the system and replaced with the SX3-128 printed fordeposition of the source and drain layer. The source/drain layer wasalso printed with Cabot Silver. The height of the printhead was adjustedto approximately 1.0 mm above the substrate and the sabre angle was setfor a resolution of 702 dpi. The source/drain layer was printed twice.

For printing of the first source/drain layer, the aluminum platen wascooled to 45° C. and registration was done in the same manner aspreviously mentioned for the dielectric layer. Once printing completed,the platen temperature was raised to 60° C. for 30 seconds. Thissintered the silver along the edges before completely sintering thematerial at a higher temperature. After 30 seconds the platentemperature was raised to 150° C. for 10 minutes.

For the second printed source/drain layer, not every image or featurewas printed twice. The drain lines were only printed once, whereas thesource pads were printed twice. The source pads were printed twice dueto non-uniformity after the sintering of the first layer. The platen wasset to 150° C. for 10 minutes to sinter the silver.

Before the process of printing the semiconductor, the platen was cooledto 30° C. and a surface treatment was applied to the dielectric materialand the source/drain contacts. High purity toluene was deposited ontothe surface of the entire sample with a pipet and left on the sample for1.0 minute. After 1.0 minute the toluene was removed by blowing it offwith an air can. Next, a solution of 1.0 mmol perfluorothiolphenol inhigh purity toluene was deposited on the surface of the entire sampleand left for 1.0 minute. The solution was removed by blowing it off withan air can. The previous step was then repeated. For the final step,high purity toluene was deposited on the entire surface of the substratefor 20 seconds. After 20 seconds the toluene was blown off the samplewith an air can. This treatment cleaned any residue on the contacts andprovided a favorable surface energy for the semiconductor solution.

Upon completion of the surface treatment, the SX3-128 printhead wasremoved from the system and replaced with an SE-128 printhead. Theprinthead was filled with solution in n-butylbenzene of 1.0 wt %polystyrene and 2.0 wt % of an organic semiconductor,6,13-bis(triisopropylsilyethynyl)pentacene. The height and sabre anglewere adjusted to the specifications previously mentioned. Registrationof the semiconductor layer was completed as previously mentioned for theother layers.

Before deposition of the semiconductor a preheat step was initiated inorder to remove any solvent, toluene, that remained on the substrateafter the surface treatment. This preheat step was completed with theonline infrared lamp at 6 passes, 2.0 in/sec and 80% power. Oncecompleted, the platen was cooled to 30° C.

As noted above, 18 drops or 540 pL of semiconductor solution wasdeposited onto each transistor.

Results

Transistors were measured with saturated I_(d)-V_(g) curves. The gatevoltage was biased from 10V to −40V and the drain voltage was set to−40V. The average mobility of transistors of Comparative Example 2C was0.042 cm²/V-s, whereas, the average mobility of transistors of Example 1was 0.11 cm²/V-s. FIG. 6 is a graph presenting mobility values fortransistors of Example 1 and Comparative Example 2C. The transistorsaccording to the present disclosure demonstrated greater mobility. FIG.7 is a graph presenting sub-threshold voltage values for transistors ofExample 1 and Comparative Example 2C. The transistors according to thepresent disclosure demonstrated reduced sub-threshold voltage. FIG. 8 isa graph presenting on/off current ratio values for transistors ofExample 1 and Comparative Example 2C. The transistors according to thepresent disclosure operated at greater on/off current ratio values.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand principles of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth hereinabove.

1. A method of making a thin film semiconductor device comprising thesteps of: a) providing a substrate bearing first and second conductivezones, wherein the first and second conductive zones define a channeltherebetween and wherein the channel does not border more than 75% ofthe perimeter of either conductive zone; and b) depositing a discretealiquot of a solution comprising an organic semiconductor adjacent to oron the channel, where the aliquot provides organic semiconductor to asingle thin film semiconductor device, where a majority of the solutionis deposited to one side of the channel and not on the channel.
 2. Themethod according to claim 1 wherein the channel does not border 50% ormore of the perimeter of either conductive zone.
 3. The method accordingto claim 1 wherein the boundaries between the channel and each of theconductive zones are substantially linear and substantially parallel. 4.The method according to claim 1 wherein the thin film semiconductordevice is a transistor, the first conductive zone is a source and thesecond conductive zone is a drain.
 5. The method according to claim 1wherein more than 70% of the solution is deposited to one side of thechannel and not on the channel.
 6. The method according to claim 1wherein more than 90% of the solution is deposited to one side of thechannel and not on the channel.
 7. The method according to claim 1wherein all of the solution is deposited to one side of the channel andnot on the channel.
 8. The method according to claim 1 wherein thediscrete aliquot is deposited in the form of a plurality of droplets. 9.The method according to claim 8 wherein the droplets are deposited byinkjet printing.
 10. The method according to claim 9 wherein at least70% of the droplets are deposited to one side of and not on the channel.11. The method according to claim 9 wherein at least 90% of the dropletsare deposited to one side of and not on the channel.
 12. The methodaccording to claim 9 wherein all of the droplets are deposited to oneside of and not on the channel.
 13. The method according to claim 1wherein the channel has a channel length and wherein the discretealiquot of a solution comprising an organic semiconductor is allowed towet out after deposition and thereupon has a length that is not morethan 10 times the channel length.
 14. The method according to claim 1wherein the channel has a channel length and wherein the discretealiquot of a solution comprising an organic semiconductor is depositedin a band having a length that is less than the channel length.
 15. Themethod according to claim 1 wherein the channel has a channel length,wherein the discrete aliquot of a solution comprising an organicsemiconductor is deposited in a band having a length that is less thanthe channel length, and wherein all of the solution is deposited to oneside of the channel and not on the channel.
 16. A thin filmsemiconductor device comprising: a) a substrate bearing first and secondconductive zones, wherein the first and second conductive zones define achannel therebetween and wherein the channel does not border more than75% of the perimeter of either conductive zone; and b) a discretesemiconductor layer comprising an organic semiconductor on and adjacentto the channel, where the discrete semiconductor layer serves a singlethin film semiconductor device, where a majority of the discretesemiconductor layer lies to one side of and not on the channel.
 17. Thedevice according to claim 16 wherein the channel does not border 50% ormore of the perimeter of either conductive zone.
 18. The deviceaccording to claim 16 wherein the boundaries between the channel andeach of the conductive zones are substantially linear and substantiallyparallel.
 19. The device according to claim 16 wherein the thin filmsemiconductor device is a transistor, the first conductive zone is asource and the second conductive zone is a drain.
 20. The deviceaccording to claim 19 additionally comprising a gate and a dielectriclayer.
 21. The method according to claim 16 wherein more than 55% of thediscrete semiconductor layer lies to one side of and not on the channel.22. The method according to claim 16 wherein more than 60% of thediscrete semiconductor layer lies to one side of and not on the channel.23. The method according to claim 16 wherein more than 70% of thediscrete semiconductor layer lies to one side of and not on the channel.24. The method according to claim 16 wherein more than 80% of thediscrete semiconductor layer lies to one side of and not on the channel.25. The device according to claim 16 wherein channel has a channellength and wherein the discrete semiconductor layer has a length that isnot more than 10 times the channel length.
 26. A method of making a thinfilm semiconductor device pair comprising the steps of: a) providing asubstrate bearing i) first and second conductive zones, wherein thefirst and second conductive zones define a first channel therebetween;and ii) third and fourth conductive zones, wherein the third and fourthconductive zones define a second channel therebetween; and b) depositinga discrete aliquot of a solution comprising an organic semiconductoradjacent to or on the first and second channels, where the aliquotprovides organic semiconductor to exactly two single thin filmsemiconductor devices, where a majority of the solution is deposited toone side of the first channel and not on the first channel, and where amajority of the solution is deposited to one side of the second channeland not on the second channel.
 27. A thin film semiconductor device paircomprising: a) a substrate bearing i) first and second conductive zones,wherein the first and second conductive zones define a first channeltherebetween; and ii) third and fourth conductive zones, wherein thethird and fourth conductive zones define a second channel therebetween;and b) a discrete semiconductor layer comprising an organicsemiconductor on and adjacent to the first and second channels, wherethe discrete semiconductor layer serves exactly two single thin filmsemiconductor devices, where a majority of the discrete semiconductorlayer lies to one side of and not on the first channel, and where amajority of the discrete semiconductor layer lies to one side of and noton the second channel.